The Verizon Novatel USB551L and the Verizon Pantech UML290VW both work.
http://forum.mikrotik.com/t/compatibility-report-verizon-novatel-usb551l-and-verizon-pantech-uml290vw/89005/1
I’m trying to get the AT&T AirCard 340U to work now but no luck so far probably because it’s stuck in MBIM mode.
Beware with all USB modems… Devices like the RB2011 may not provide enough power on their USB-OTG ports to reliably power the modem. An external power supply or powered hub might be required. The devices will full size USB-A connectors are no problem.
If the device you’re going to deploy has a mini-PCIe slot, your better bet is to use a Sierra MC7354 card. You can flash them to Verizon, AT&T, Sprint, Rogers, Telus or Generic firmware. The Generic may work with T-Mobile but not sure. I have them deployed with both Verizon and AT&T config.
http://forum.mikrotik.com/t/compatibility-report-sierra-mc7354-mini-pcie-lte/88870/1